It has already been proposed to provide timepieces having the usual time indicating hands with digital means for indicating information such as dates or time interval settings. Purely mechanical arrangements in this respect have been known for many years at least in respect of date indicating arrangements and no particular difficulty is experienced when it comes to synchronizing date changes with the hour displayed. Thus normally in such time pieces the arrangement is such that the date changes at midnight.
With the advent of electronic timepieces, particularly wrist watches, the problem arises of providing synchronization between an electro-mechanical arrangement on the one hand and a purely electronic arrangement on the other. Although such dual display timepieces have been produced, the problem of synchronization has to the present time not been satisfactorily resolved.
It is realized for instance that the electronic portion of such timepieces generally includes various registers which provide volatile storage of data. Thus at any time when the energizing current is cut off, as for instance when the battery in a wrist watch is replaced, the data within such registers disappears immediately and before the instrument becomes fully useful it must be completely re-synchronized. It is likewise desirable to enable maintaining of synchronization taking into account that this may be lost to a slighter degree merely through the inherent difference between electro-mechanical and purely electronic arrangements.
Known solutions to this problem have provided, among others, a system in which the watch hands are set at 12:00 (=24:00), then by pressing on one or several switches the digital display may be synchronized. The known arrangement, although needing only to be used after power failure (in the case of a wrist watch following battery change) constitutes a complex set of operations which might well be beyond the capacity of the average person.
A further possibility might provide a switch actuated by a cam which could represent the position of the hands at midnight. The difficulty with such arrangement resides in its obvious lack of precision and probable lack of reliability.
The solution proposed by the present invention provides a synchronization system which will go into operation automatically following cutting and restoring of the current as in the case of a wrist watch when the battery is changed. Other applications of the system will be discussed hereinafter in the description to follow.